Summary of work: Age-related changes in bone mass have been demonstrated in both men and women. Age and sex related differences hormones, nutritional and physiological variables involved in bone turnover are important in elucidating changes in bone physiology in normal aging and disease. Specifically, the relationship age and sex to changes in body composition, both as a marker of obesity and as a measure of the weight- bearing load on bone are important factors in bone status and rates of change. The most dramatic rates of change in bone mass occur at the menopause, and changes of body composition, bone mass, and bone markers and hormones are being investigated in 100 women aged 45-55 who have been recruited to the Baltimore Longitudinal Study of Aging as part of the perimenopausal cohort. These women, who were still menstruating, on entry to the study, will be followed at 3month intervals as they traverse the menopause, and for two years since their last period. These studies will allow for the interpretation of the changes that occur prior to and immediately around the time of the cessation of menses, changes that can only be appreciated in a prospective longitudinal study. Within the BLSA the loss of femoral neck bone mineral density has been studied in 315 men and 323 women who had been followed for at least 4 years (maximum 10 year follow up). All women and all but the youngest and oldest men had significant bone loss. Only the 50 year old women were losing bone at a significantly greater rate than men. Both men and women are losing bone across the age span, with no significant acceleration of bone loss with age in either sex.